A magnetic head assembly including separate read and write head elements or islands is the recording and reproducing unit of a magnetic tape drive system. An island may include one or more magnetic cores. A magnetic coil is wound around the magnetic core of each read and write island, and each core has a gap. During the recording process, electric current supplied to a coil produces a magnetic field in the write core. The resulting flux across the gap region enters a magnetic tape moving over the island and magnetizes a small area therein in accordance with the direction of the current. During the reproducing process, the magnetized areas induce magnetic flux in the read core and an associated voltage in the coil.
The bit density is a measure of the number of magnetized flux reversals recorded per unit length or area on a magnetic tape. High bit density is desired for the tape in order to provide high data capacity. At high bit recording densities, the separation between the gap of an island and the moving tape must be maintained within very narrow tolerances, e.g. less than 2 microinches, to achieve proper retrieval and recording of the closely-spaced bits; slight variations in the separation between the gap and tape can lead to erratic recording performance. Yet for low-to-moderate bit densities, a larger separation, e.g. 10-20 microinches, is tolerable because the bits are spaced farther apart.
Previously, magnetic tapes having a thickness of at least 1.0 mil (0.001 inch) were widely used in tape drives. These tapes are composed of materials having microstructural properties that result in scratching of the outer surfaces of the islands and eventual wear of the head assembly. Advances in recording material technology have led to thinner tapes having a thickness of 0.5 mil (0.0005 inch) or less and capable of achieving high bit densities. The thin tapes have largely replaced the thicker tapes because they provide higher storage capability per volume of tape. Moreover, the materials of the thinner tapes are smoother, thus increasing the operating life of the head. Yet, there is still a need to read the thicker tapes, since they often contain data that must be retrieved from them.
A magnetic head assembly configured to operate with tapes of different thicknesses may encounter data reliability problems. Movement of a tape over the head assembly gradually wears the contour of the head to the "natural radius of curvature" of the tape. The inherent stiffness of a tape influences its natural curvature, i.e. thick tapes are typically stiffer than thin tapes and thus, have a larger natural radius at constant tension. A head assembly partially shaped to the curvature of a thick tape has a large tape-to-head separation at the center of the island, where the gap is located, when operating with thinner tapes. The thick tape is also likely to scratch the surface of the head, particularly in the area of the gap. The increased separation and scratches significantly reduce the amplitude of signals retrieved from the thin tape.
Therefore, an object of the present invention is to provide a magnetic contact head assembly capable of recording and retrieving data on magnetic tapes of different thicknesses.
Another object of the present invention is to minimize the separation between the gap of an island and a thin magnetic tape having a high bit density so as to facilitate proper recording and retrieval performance.
Additionally, an object of the present invention is to provide controlled separation between the gap of an island and a thick magnetic tape having a low bit density so as to minimize damage to the gap, yet still maintain proper recording performance.